1. Field of the Invention
The present invention relates to an optical scanning apparatus, and also to an image forming apparatus provided with such an optical scanning apparatus.
2. Description of the Related Art
In an optical scanning apparatus, conventionally, a rotary polygon mirror as light deflecting member, an Fθ lens or an Fθ mirror as a scanning optical element, and a photosensitive drum as a medium to be scanned are generally used. The shape of the Fθ lens or the Fθ mirror is optimized so that a light beam on the photosensitive drum attains speed uniformity or substantial speed uniformity with respect to the rotary polygon mirror which is rotated at a constant speed (for example, see JP-A-2001-056445 (Abstract)).
The scanning position may be deviated because of, for example, relative positional deviation between the Fθ lens and the photosensitive drum. In such a case, the scanning position is sometimes adjusted by controlling the delay time from detection of the horizontal synchronizing signal to minutely correct the scanning angle (for example, see JP-A-5-136951 (Abstract) and JP-A-2002-202648 (Abstract)). However, there is a problem in that speed uniformity of the light beam on the photosensitive drum after the adjustment is changed from that before the adjustment, and therefore the accuracy is lowered.